A possible alternate energy source that we haven't discussed on this thread as a mode to generate H2 is the thermal gradient in the ocean. By using the hot upper level waters to expand a working fluid through a turbine and the cooler lower level waters to contract / condense the working fluid, there is a near-limitless source of "free energy" for oil drilling spars in deep waters.
One paper published online proposes that the thermal gradient could be used for energy generation, H2 producton and liquefaction for storage. see link
Ongoing Kalina Cycle Developments